1. Field of the Invention
The present invention relates to a method for manufacturing an organic EL device, and more particularly to a method for an organic EL device in a preferred environment in which respective manufacturing steps are executed.
2. Description of the Related Art
FIG. 2 is a perspective view of a conventional EL display panel 25 provided with an organic EL device. In the EL display panel 25, a plurality of strip-shaped transparent electrodes 11 of ITO (Indium Tin Oxide) (hereinafter referred to as ITO transparent electrodes) are arranged on a glass substrate 2 in a direction of arrow 93. Above the ITO transparent electrodes, a plurality of strip-shaped organic layers 12 are arranged in a direction of arrow 94.
A plurality of strip-shaped upper electrodes 13 made of metal film patterns such as Al, Mg, Ag etc are superposed on the organic layers 12, respectively. The ITO transparent electrodes 11, organic EL layers 12 and upper electrodes 13 are covered with a sealant (not shown) on the glass substrate 2. The internal space of the sealant is filled with nitrogen.
In the EL display panel 25, when a voltage is applied between a prescribed ITO transparent electrode 11 and a prescribed upper electrode 13, an organic EL layer 12 located at an area where these electrodes cross is activated by the voltage emits light. Therefore, by controlling selection of each ITO transparent electrode 11 and each upper electrode 13, a desired display can be realized using the EL display panel 25.
An explanation will be given of a method of manufacturing such a conventional organic EL device. Generally, a glass substrate 2 coated with ITO is prepared. The glass substrate 2 is etched through a mask pattern of photoresist to form the ITO transparent electrode 11 having a prescribed pattern. With the glass substrate 2 with the ITO transparent electrode formed thereon being placed in a vacuum, the organic layer 12 and upper electrode 13 are formed by the vacuum evaporation technique. Thereafter, they are sealed by the sealant secured to the glass substrate 2 in a nitrogen atmosphere. In this way, the organic layer 12 and upper electrode 13 are formed in a vacuum and sealed in the nitrogen atmosphere, thus preventing moisture from intruding into the inner space of the sealant.
However, the conventional method of manufacturing an organic EL device is accompanied by deposition of some impurities to the ITO transparent electrode. Specifically, since the ITO transparent electrode 11 is formed through the etching using photoresist, with the impurities such as water and so on, being applied to the surface of the ITO transparent electrode 11, the organic layer 12 is formed on the ITO transparent electrode 11.
Generally, deposition of impurities on the ITO transparent electrode 11 changes a potential at the surface of the ITO transparent electrode 11 to vary a device characteristic. Unlike an inorganic EL device which operates at a high voltage of e.g. 100 V, the organic EL device can operate at a low voltage of several volts. Therefore, if the device characteristic varies and incorrect operation is easy to be generated because of a slight change in the potential at the surface of the ITO transparent electrode 11, an expected correct operation of the organic EL device cannot be realized. This largely attenuates reliability of the organic EL device.
An object of the present invention is to provide an organic EL device with improved reliability.
In order to attain the above object, in accordance with a first aspect of the present invention, there is provided a method of manufacturing an organic EL device comprising the steps of: forming a lower electrode formed on a substrate; forming an organic EL layer formed on the lower electrode; and forming a upper electrode formed on the organic EL layer; wherein at least the step of forming the lower electrode is executed in an environment not exposed to the outside air or in a vacuum.
In this configuration, it is possible to prevent impurities from being applied to the lower electrode so that changes of the characteristic of the EL element can be avoided, thereby improving the reliability of the organic EL device.
A second aspect of the method is a method according to the first aspect, wherein all these steps are executed in an environment not exposed to the outside air.
In this configuration, since all the above steps are executed in an environment not exposed to the outside air, it is possible to prevent impurities impeding the operation of the device from being applied to the respective layers so that changes of the characteristic of the EL device can be avoided, thereby providing a highly reliable organic EL device. Particularly, this prevents the impurities from being applied to the ITO transparent electrode so that changes of the characteristic of the EL display panel can be avoided and change of a stationary state can be reduced, thereby the reliability and reappearance of the organic EL device are improved.
A third aspect of the method is a method according to the first aspect, wherein all these steps are executed in a vacuum.
In this configuration, it is possible to prevent impurities impeding the operation of the device from being applied to the respective layers so that changes of the characteristic of the EL device can be avoided, thereby providing a highly reliable organic EL device. Particularly, this prevents the impurities from being applied to the ITO transparent electrode so that changes of the characteristic of the EL display panel can be avoided, thereby improving the reliability of the organic EL device.
The fourth aspect, in a method of manufacturing an organic EL device according to the second aspect, is characterized in that said lower and upper electrodes are formed in stripe patterns which are apart from one another so that a large number of organic EL devices are arranged in a matrix. In this configuration, the organic EL panel having a device characteristic with no variation can be manufactured.
The fifth aspect, in a method of manufacturing an organic EL device according to the second aspect, is characterized in that the step of forming the lower electrode is to form an electrode pattern of ITO (indium-tin-oxide) on a glass substrate. The characteristic of the organic EL device varies greatly depending on the surface state of ITO. However, in accordance with the method of the present invention, the layer is deposited without being exposed to outside air so that it possible to prevent stain or humidity from being applied on the surface of ITO, thus providing a highly reliable organic EL device.
The sixth aspect, in a method of manufacturing an organic EL device according to the first aspect, is characterized in that the step of making said lower electrode is performed by a vacuum evaporation through a mask a the substrate. In this method, evaporation in carried out through a shadow mask of e.g. metal so that a desired thin film can be formed. In addition, a pattern of the lower electrode with a gently-sloping edge can be obtained so that concentration of an electric field can be prevented. This permits the life of the device to be lengthened.
The seventh aspect, in a method of manufacturing an organic EL device according to the sixth aspect, is characterized in that the step of making said organic EL layer in performed by a vacuum evaporation through a mask on the substrate.
The eighth aspect, in a method of manufacturing an organic EL device according to the seventh aspect, in characterized in that the step of making said upper electrode is performed by a vacuum evaporation through a mask on the substrate. In this method, evaporation is carried out through a shadow mask of e.g. metal so that a desired thin film can be formed. In addition, a pattern of the upper electrode with a gently-sloping edge can be obtained.
The ninth aspect, in a method of manufacturing an organic EL device defined in the first aspect, the steps of forming said lower electrode, organic EL layer and upper electrode are successively performed by selectively activating evaporation sources in the same deposition chamber. According to this method, deposition can be continuously carried out in a state where the substrate and evaporation source are at a standstill. Thus, the clean surface state of the substrate can be maintained to form respective film with good quality.
The tenth aspect, in a method of manufacturing an organic EL device defined in the first aspect, is characterized in that the steps of forming the lower electrode, organic EL layer and upper electrode include the step of transporting the substrate into deposition chambers, respectively without being exposed to outside air. This method permits the film deposition to be carried out successively and effectively.
The eleventh aspect, in a method of manufacturing an organic EL device defined in the first aspect, is characterized in that the steps of forming the lower electrode, organic EL layer and upper electrode include the step of successively transporting the corresponding evaporation source to the substrate. Thus, only the evaporation source moves with the substrate being at a standstill so that the substrate is maintained in a stable state to prevent impurities from being applied to the substrate.
The twelfth aspect, in a method of manufacturing an organic EL device defined in the eleventh aspect, is characterized in that the substrate is located at a higher position than the evaporation source in a reactive chamber. Thus, impurities applied to the evaporation source do not fall onto the substrate, thus providing the preferable surface state of the substrate.
The above and other objects and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings.